The prime movers of ankle plantar flexion are the soleus and gastrocnemius muscles. These muscles are located at the back of the lower leg and attach from the knee to the heel.
The gastrocnemius and soleus together are called the triceps surae. Together, they form a complex of three muscles, because the gastrocnemius has two heads that attach from the knee to the foot through the Achilles tendon. The soleus attaches to the two lower leg bones, the tibia and fibula. The soleus and gastrocnemius fold around each other, forming a bulge with a cleft at the calf when the muscles are well-developed.
Many muscles assist with plantar flexion of the ankle, a movement akin to pointing the toes. The synergist muscles assist the flexion. Antagonist muscles lengthen as the prime movers shorten during flexion. The major antagonist is the tibialis anterior, or the shin muscle. The posterior tibialis and the medial, or inner, gastrocnemius work to neutralize the force during plantar flexion of the ankle. The fibularis muscles stabilize the ankle during plantar flexion. In dorsiflexion, or pulling the toes up, the roles of prime mover and antagonist are reversed. The prime mover in dorsiflexion is the tibialis anterior and the antagonists include the soleus and gastrocnemius muscles.